Coating powders having a resin system of carboxyl-functional polyester and an epoxy curative, such as triglycidyl isocyanurate (TGIC), are known, e.g., as noted in U.S. Pat. No. 5,187,220. Typical of a polyester for use in such a coating would be a polymer based on terephthalic acid (TA), neopentyl glycol (NPG) and some small amount of modifying monomer, such as ethylene glycol (EG), 1,4-butanediol (1,4-BD), 1,6-hexane diol (1,6-HD), isophthalic acid (IPA), phthalic acid (PA), adipic acid (AA), succinic acid (SA), trimethylol propane (TMP), trimellitic anhydride (TMA), etc.
Many prior art epoxy-cured polyester coating powders, particularly those containing polyesters based primarily on NPG and TA, suffer from the undesirable phenomenon called blooming. The blooming effect becomes evident when an object coated with such a coating powder is kept for a sufficient length of time at a temperature above the glass transition temperature (T.sub.g), the bloom appearing as a whitish patina on the surface.
It is a primary object of the invention to provide an epoxy-cured polyester coating powder that does not bloom.